CC2 HMA Overlay Post Traffic Testing

Test Results for CBR & Plate Load Testing

The test results from different pavement layers in the four trenches are summarized in Table 1. One of the significant observations relative to Table 1 was made from the subgrade CBRs in the four trenches. Pre-traffic/pre-overlay measurements of subgrade strength in the test pits showed that water had migrated from the crushed aggregate subbase into the subgrade of MRC and softened the top 3 or so inches of the subgrade. The CBR at the subgrade surface in the MRC test pits was approximately 4, whereas the CBR at 1 foot (30 cm) below the subgrade surface was approximately 6 to 8. The MRG subgrade surface CBR was high (about 11). It was assumed that this was due to water being drawn from the subgrade (since the slabs were directly cast over subgrade) by hydration of the concrete during curing. This phenomenon was not observed in MRC (slab over crushed stone base) or MRS (slab over econocrete subbase). The results from trenches confirmed the observations/measurements from the pre-traffic test pits.

Also, performing any type of strength tests just on the rubblized material is very difficult (if not impossible) because of the nature of the material. In this project, plate load tests were performed on the top of the rubblized layer. Due to severe rutting in MRC, plate load tests could not be performed inside the traffic path.

In test item MRG, the ‘k’ value from the plate load test inside the traffic path was lower (k = 322 pci (87.26 kPa/mm)) than the k value outside the traffic path test (k = 457 pci (123.85 kPa/mm)).  The lower k value inside the traffic path could be the result of incipient failure in MRG.

In test item MRS, the k value from the plate load test inside the traffic path was higher (k = 780 pci (211.38 kPa/mm)) than the k value outside the traffic path test (k = 579 pci (156.91 kPa/mm)).

Table 1. Summary of Test Results from Trenching Study

MC – Moisture Content

As Constructed Moisture Content for subgrade – 30.7%.

1 pcf = 16.018 kg/m³

1 pci = 0.271 kPa/mm